The need to reduce fuel consumption and engine exhaust emissions from vehicles powered by internal combustion engines is well known. Hybrid gasoline-electric vehicles achieve high fuel efficiency and low emissions by combining highly efficient internal combustion gasoline engines with electric motors. Although the mechanical means by which the electric motors and gasoline engines are coupled to the drive trains varies between vehicle manufacturers, hybrid electric vehicles utilize both the gasoline engines and the electric motors to power the driving wheels to some extent. The engine control system of a hybrid vehicle varies the amount of drive power from the electric motor and the gasoline engine depending on the necessary power output and the driving conditions, selecting the most efficient method of powering the vehicle for the situation at hand.
In general, minimizing the use of the gasoline engine of a hybrid vehicle at inefficient periods such as when the vehicle is temporarily stopped enhances fuel efficiency. Such vehicles increase their fuel efficiency by shutting off the gasoline engine at extended stops, such as at stop signs or stoplights and then restarting the gasoline engine when it is desired to propel the vehicle. This is known as an Engine Stop Start (ESS) function. When the gasoline engine is off, auxiliary systems such as the radio, gauges, power windows, and the like are kept operative by a low voltage (usually 12 volt) electrical system. When the stoplight changes or when it is otherwise safe to proceed, in response to the brake pedal being released and/or the accelerator pedal being depressed, the gasoline engine is immediately restarted and the vehicle can drive off.
Such ESS operation is beneficial in reducing fuel use and emissions but makes operation of a conventional climate cooling system difficult. The passenger cabin air conditioning system does not work without some kind of power input. The compressor that powers the Air Conditioning (A/C) system is generally driven by the crankshaft of the gasoline engine, and therefore is inoperative when the gasoline engine is shut off at the stoplights or stop signs, for instance. Without the compressor running, pressure differentials within the A/C system, that are necessary for the A/C system to function, quickly decrease, eliminating the cooling ability thereof. Without the cooling ability of the A/C system, the air circulating through the passenger cabin increases in temperature and quickly becomes uncomfortably warm if the ambient temperature outside of the vehicle is high. In addition, after a few seconds, the cabin air might also begin to have a musty smell because moisture is no longer being removed from the cabin air by the compressor to the extent it was being removed when the compressor was running.
Conventional hybrid electric vehicles deal with the forgoing ESS climate cooling control problem in a number ways. One method is to simply take no action. When the vehicle arrives at a stop sign or stoplight, the gasoline engine is turned off, and the vehicle provides the occupants of the passenger cabin with no additional cooling until the gasoline engine is again started. This approach is economical, but will lead to uncomfortable conditions for the vehicle passengers when the ambient temperature of the vehicle is high. Another approach to the ESS climate cooling control problem is to keep the gasoline engine running at stoplights or stop signs when A/C is requested. Keeping the engine running allows the climate cooling system to continue providing the passenger cabin with cooling, but contributes nothing to fuel efficiency or emission reduction when A/C is required because the gasoline engine is still operating and consuming fuel. Hence, this approach undesirably sacrifices fuel efficiency for passenger comfort.
Another prior art solution to the ESS climate cooling control problem proposes the addition of a dedicated electrical motor as the sole power source for driving the A/C compressor. Unfortunately, since this system has to be able to provide the entire passenger cabin cooling, even on very hot days, it requires a high power (numerous kilowatts (kW)) motor and costly electronics such as an expensive power-inverter system. In addition, the expensive high power, dedicated electric motor adds undesired mass to the vehicle.
Still another approach to dealing with the ESS problem is employed by some “mild” gasoline-electric hybrid vehicles that have a combined electric starter motor and generator/alternator (MoGen) that supports the hybrid and ESS functionality. The MoGen replaces the conventional starter motor and alternator with one unit that performs both functions. The MoGen system is implemented to enable the fuel-cut off feature while minimally affecting “driveability”. When the vehicle is decelerating or is stopped, the fuel flow to the engine is stopped by the ESS system. In a mild hybrid vehicle having a powertrain with an automatic transmission, after the vehicle engine has been temporarily shut down, then either after the passage of a selected amount of time or a brake-pedal release the MoGen spins up and restarts the gasoline engine. If it is desired for the vehicle to start going from a stop, the spin up of the engine can “creep” the vehicle forward similar to the action of the automatic transmission of a conventional vehicle while the engine is being restarted. When the engine is running the MoGen acts as a generator or alternator to supply the vehicle's electrical power requirements and to recharge the batteries.
In some prior art systems the MoGen unit is typically belted to the crankshaft pulley of the engine so that it can perform the engine start or automatic restart, vehicle creep and charging functions. If the crankshaft pulley is clutched to the gasoline engine crankshaft, the associated belt driven components can be driven by the MoGen electric motor when the engine is in the temporarily shutoff state without driving the engine. Specifically, a mild hybrid system has been utilized in which the crankshaft pulley is de-clutched from the crankshaft allowing the MoGen to utilize battery-supplied power to turn the entire accessory drive system independent of the engine. However, the accessory drive system can also include the hydraulic power steering pump, water pump, and an array of idler pulleys in addition to the A/C compressor. The operation of the compressor allows the passenger compartment to continue to receive cooling airflow with the engine temporarily shutoff; however, the maximum fuel efficiency of the mild hybrid vehicle is compromised because of the large amount of battery energy that is expended spinning the other accessory drive system components. The MoGen must replenish this battery energy at some later time when the engine is running. This replenishment can provide an undesirably high load on the engine. It is desirable to maintain both fuel efficiency and passenger comfort. Thus this approach again sacrifices fuel efficiency for passenger comfort. In addition, this approach requires complicated clutch/drive mechanisms, which increase vehicle cost and whose failure modes could affect the base-engine hardware functions.
In view of the foregoing, it should be appreciated that there is a need to provide methods and apparatus for providing simple, efficient and economical motor vehicle passenger cabin climate cooling control systems and methods for use in hybrid and mild hybrid electric vehicles. Such systems and methods should also minimize the parts count and parts mass required for powering the A/C compressor when the engine is temporarily inoperative because of ESS operation, for instance. Moreover, such systems and methods should ensure that the vehicle driveability is consistent, predictable and pleasing to the customer while maintaining fuel efficiency and emissions reductions.
Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description, brief summary, abstract, and appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.